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Presence of mRNA for glutamic acid decarboxylase in both excitatory and inhibitory neurons
Y Cao1, K S Wilcox, C E Martin
1Department of Pharmacology, University of Pennsylvania, Philadelphia 19104, USA.
Abstract:
Neurons in very low density hippocampal cultures that are physiologically identified as either GABAergic inhibitory or glutamatergic excitatory all contain mRNA for the gamma-aminobutyric acid (GABA) synthetic enzyme, glutamic acid decarboxylase (GAD), as detected by single cell mRNA amplification and PCR. However, consistent with the physiology, immunocytochemistry revealed that only a subset of the neurons stain for either GAD protein or GABA. A similar fraction hybridize with RNA probes for GAD65 and GAD67. Hippocampal CA1 pyramidal neurons in slice preparations, which are traditionally thought to be excitatory, also contain mRNA for GAD65 and GAD67. Hippocampal neurons in culture did not contain mRNA for two other neurotransmitter synthesizing enzymes, tyrosine hydroxylase, and choline acetyl transferase. These data suggest that in some neurons, presumably the excitatory neurons, GAD mRNA is selectively regulated at the level of translation. We propose that neurotransmitter phenotype may be posttranscriptionally regulated and neurons may exhibit transient phenotypic plasticity in response to environmental influences.
Insights
All hippocampal neurons, both inhibitory and excitatory, contain messenger RNA for the GABA synthetic enzyme glutamic acid decarboxylase (GAD). However, only a subset express GAD protein, suggesting post-transcriptional regulation of neurotransmitter phenotype.
Area of Science:
- Neuroscience
- Molecular Biology
- Cellular Neuroscience
Background:
- Neurons are classified as inhibitory (GABAergic) or excitatory (glutamatergic) based on their primary neurotransmitter.
- The synthesis of gamma-aminobutyric acid (GABA) is primarily mediated by the enzyme glutamic acid decarboxylase (GAD).
Purpose of the Study:
- To investigate the expression of GAD mRNA and protein in different types of hippocampal neurons.
- To explore the regulation of neurotransmitter phenotype in neurons.
Main Methods:
- Single-cell mRNA amplification and PCR to detect GAD mRNA in cultured hippocampal neurons.
- Immunocytochemistry to identify GAD protein and GABA localization.
- Hybridization with RNA probes for GAD65 and GAD67.
- Analysis of hippocampal CA1 pyramidal neurons in slice preparations.
Main Results:
- All physiologically identified GABAergic and glutamatergic neurons in culture expressed GAD mRNA.
- Only a subset of neurons showed detectable GAD protein or GABA, correlating with physiological type.
- Hippocampal CA1 pyramidal neurons (traditionally excitatory) also contained GAD65 and GAD67 mRNA.
- Neurons in culture did not express mRNA for tyrosine hydroxylase or choline acetyl transferase.
Conclusions:
- GAD mRNA is present in both inhibitory and excitatory hippocampal neurons, but GAD protein expression is selective.
- This suggests that GAD mRNA levels are regulated post-transcriptionally, likely at the translational level, in excitatory neurons.
- Neurotransmitter phenotype may be plastic and subject to post-transcriptional regulation, potentially influenced by environmental factors.